Inferring Stochastic Rates from Heterogeneous Snapshots of Particle Positions.

Many imaging techniques for biological systems-like fixation of cells coupled with fluorescence microscopy-provide sharp spatial resolution in reporting locations of individuals at a single moment in time but also destroy the dynamics they intend to capture. These snapshot observations contain no information about individual trajectories, but still encode information about movement and demographic dynamics, especially when combined with a well-motivated biophysical model. The relationship between spatially evolving populations and single-moment representations of their collective locations is well-established with partial differential equations (PDEs) and their inverse problems. However, experimental data is commonly a set of locations whose number is insufficient to approximate a continuous-in-space PDE solution. Here, motivated by popular subcellular imaging data of gene expression, we embrace the stochastic nature of the data and investigate the mathematical foundations of parametrically inferring demographic rates from snapshots of particles undergoing birth, diffusion, and death in a nuclear or cellular domain. Toward inference, we rigorously derive a connection between individual particle paths and their presentation as a Poisson spatial process. Using this framework, we investigate the properties of the resulting inverse problem and study factors that affect quality of inference. One pervasive feature of this experimental regime is the presence of cell-to-cell heterogeneity. Rather than being a hindrance, we show that cell-to-cell geometric heterogeneity can increase the quality of inference on dynamics for certain parameter regimes. Altogether, the results serve as a basis for more detailed investigations of subcellular spatial patterns of RNA molecules and other stochastically evolving populations that can only be observed for single instants in their time evolution.

Minimal Mechanisms of Microtubule Length Regulation in Living Cells.

The microtubule cytoskeleton is responsible for sustained, long-range intracellular transport of mRNAs, proteins, and organelles in neurons. Neuronal microtubules must be stable enough to ensure reliable transport, but they also undergo dynamic instability, as their plus and minus ends continuously switch between growth and shrinking. This process allows for continuous rebuilding of the cytoskeleton and for flexibility in injury settings. Motivated by in vivo experimental data on microtubule behavior in Drosophila neurons, we propose a mathematical model of dendritic microtubule dynamics, with a focus on understanding microtubule length, velocity, and state-duration distributions. We find that limitations on microtubule growth phases are needed for realistic dynamics, but the type of limiting mechanism leads to qualitatively different responses to plausible experimental perturbations. We therefore propose and investigate two minimally-complex length-limiting factors: limitation due to resource (tubulin) constraints and limitation due to catastrophe of large-length microtubules. We combine simulations of a detailed stochastic model with steady-state analysis of a mean-field ordinary differential equations model to map out qualitatively distinct parameter regimes. This provides a basis for predicting changes in microtubule dynamics, tubulin allocation, and the turnover rate of tubulin within microtubules in different experimental environments.

Minimal Mechanisms of Microtubule Length Regulation in Living Cells.

The microtubule cytoskeleton is responsible for sustained, long-range intracellular transport of mRNAs, proteins, and organelles in neurons. Neuronal microtubules must be stable enough to ensure reliable transport, but they also undergo dynamic instability, as their plus and minus ends continuously switch between growth and shrinking. This process allows for continuous rebuilding of the cytoskeleton and for flexibility in injury settings. Motivated by in vivo experimental data on microtubule behavior in Drosophila neurons, we propose a mathematical model of dendritic microtubule dynamics, with a focus on understanding microtubule length, velocity, and state-duration distributions. We find that limitations on microtubule growth phases are needed for realistic dynamics, but the type of limiting mechanism leads to qualitatively different responses to plausible experimental perturbations. We therefore propose and investigate two minimally-complex length-limiting factors: limitation due to resource (tubulin) constraints and limitation due to catastrophe of large-length microtubules. We combine simulations of a detailed stochastic model with steady-state analysis of a mean-field ordinary differential equations model to map out qualitatively distinct parameter regimes. This provides a basis for predicting changes in microtubule dynamics, tubulin allocation, and the turnover rate of tubulin within microtubules in different experimental environments.

Inferring stochastic rates from heterogeneous snapshots of particle positions.

Many imaging techniques for biological systems - like fixation of cells coupled with fluorescence microscopy - provide sharp spatial resolution in reporting locations of individuals at a single moment in time but also destroy the dynamics they intend to capture. These snapshot observations contain no information about individual trajectories, but still encode information about movement and demographic dynamics, especially when combined with a well-motivated biophysical model. The relationship between spatially evolving populations and single-moment representations of their collective locations is well-established with partial differential equations (PDEs) and their inverse problems. However, experimental data is commonly a set of locations whose number is insufficient to approximate a continuous-in-space PDE solution. Here, motivated by popular subcellular imaging data of gene expression, we embrace the stochastic nature of the data and investigate the mathematical foundations of parametrically inferring demographic rates from snapshots of particles undergoing birth, diffusion, and death in a nuclear or cellular domain. Toward inference, we rigorously derive a connection between individual particle paths and their presentation as a Poisson spatial process. Using this framework, we investigate the properties of the resulting inverse problem and study factors that affect quality of inference. One pervasive feature of this experimental regime is the presence of cell-to-cell heterogeneity. Rather than being a hindrance, we show that cell-to-cell geometric heterogeneity can increase the quality of inference on dynamics for certain parameter regimes. Altogether, the results serve as a basis for more detailed investigations of subcellular spatial patterns of RNA molecules and other stochastically evolving populations that can only be observed for single instants in their time evolution.

Dexamethasone versus methylprednisolone for critical asthma: A single center, open-label, parallel-group clinical trial.

BACKGROUND: Evidence for the use of dexamethasone for pediatric critical asthma is limited. We sought to compare the clinical efficacy and safety of dexamethasone versus methylprednisolone among children hospitalized in the pediatric intensive care unit (PICU) for critical asthma. METHODS: A prospective, single center, open-label, two-arm, parallel-group, nonrandomized trial among children ages 5-17 years hospitalized within the PICU from April 2019 to December 2021 for critical asthma consented to receive methylprednisolone (standard care) or dexamethasone (intervention) at a 2:1 allocation ratio, respectively. The intervention arm received intravenous dexamethasone 0.25 mg/kg/dose (max: 15 mg/dose) every 6 h for 48 h and the standard care arm intravenous methylprednisolone 1 mg/kg/dose every 6 h (max dose: 60 mg/dose) for 5 days. Study endpoints were clinical efficacy (i.e., length of stay [LOS], continuous albuterol duration, and a composite of adjunctive asthma interventions) and safety (i.e., corticosteroid-related adverse events). RESULTS: Ninety-two participants were analyzed of whom 31 were allocated to the intervention arm and 61 the standard care arm. No differences in demographics, clinical characteristics, or acute/chronic asthma severity indices were observed. Regarding efficacy and safety endpoints, no differences in hospital LOS, continuous albuterol duration, adjunctive asthma intervention rates, or corticosteroid-related adverse events were noted. Compared to the intervention arm, participants in the standard care arm more frequently were prescribed corticosteroids at discharge (72% vs. 13%, p < 0.001). CONCLUSIONS: Among children hospitalized for critical asthma, dexamethasone appears safe and warrants further investigation to fully assess clinical efficacy and potential advantages over commonly applied agents such as methylprednisolone.

Palmitate-mediated disruption of the endoplasmic reticulum decreases intracellular vesicle motility.

Essential cellular processes such as metabolism, protein synthesis, and autophagy require the intracellular transport of membrane-bound vesicles. The importance of the cytoskeleton and associated molecular motors for transport is well documented. Recent research has suggested that the endoplasmic reticulum (ER) may also play a role in vesicle transport through a tethering of vesicles to the ER. We use single-particle tracking fluorescence microscopy and a Bayesian change-point algorithm to characterize vesicle motility in response to the disruption of the ER, actin, and microtubules. This high-throughput change-point algorithm allows us to efficiently analyze thousands of trajectory segments. We find that palmitate-mediated disruption of the ER leads to a significant decrease in vesicle motility. A comparison with the disruption of actin and microtubules shows that disruption of the ER has a significant impact on vesicle motility, greater than the disruption of actin. Vesicle motility was dependent on cellular region, with greater motility in the cell periphery than the perinuclear region, possibly due to regional differences in actin and the ER. Overall, these results suggest that the ER is an important factor in vesicle transport.

Dexamethasone for Pediatric Critical Asthma: A Multicenter Descriptive Study.

BACKGROUND: Systemic corticosteroids are vital to critical asthma management. While intravenous methylprednisolone is routinely used in the pediatric intensive care unit (PICU) setting, recent data supports dexamethasone as an alternative. Using the Pediatric Health Information System (PHIS) registry, we assessed trends and variation in corticosteroid prescribing among children hospitalized for critical asthma. METHODS: We performed a multicenter retrospective cohort study using PHIS data among children 3-17 years of age admitted for critical asthma from 2011 through 2019. Primary outcomes were corticosteroid prescribing rates by year and participating sites. Exploratory outcomes were corticosteroid-related adverse effects, rates of adjunctive pharmaceutical and respiratory interventions, mortality and length of stay. RESULTS: Of the 49 children's hospitals assessed, 26 907 encounters were included for study. Mean dexamethasone exposure rates were 18.1 ± 2.4% where 2.4 ± 1.2% represented dexamethasone-alone prescribing. Dexamethasone alone prescribing exhibited a linear trend (annual increase of 0.5 ± 0.1% annually R2 = 0.845) without correlation to cumulative site critical asthma admission rates. Compared to encounters prescribed solely methylprednisolone or a combination of dexamethasone and methylprednisolone, subjects provided dexamethasone alone had reduced asthma severity indices, length of stay, and exposure rates to adjunctive asthma interventions. Adverse events were rare and the dexamethasone-alone group less frequently experienced gastritis and hyperglycemia. CONCLUSIONS: In this multicenter retrospective study from 49 children's hospitals, dexamethasone prescribing rates appear increasing for pediatric critical asthma. Observed variability in corticosteroid prescribing implies a continued need for controlled prospective comparative analyses to define ideal corticosteroid regimens for pediatric critical asthma.

Stress Ulcer Prophylaxis for Critical Asthma.

BACKGROUND: Children hospitalized for critical asthma (CA) in the pediatric ICU (PICU) are commonly prescribed stress ulcer prophylaxis (SUP) to mitigate risk of gastrointestinal (GI) bleeding. We sought to describe trends for SUP prescribing and explore for differences in rates of GI bleeding, gastritis, and SUP-related complications for those with and without SUP exposure. METHODS: We performed a retrospective, multicenter cohort study using the Pediatric Hospital Information System registry among 42 children's hospitals from 2010 to 2019 including children 3 to 17 years of age admitted to the PICU for CA. Primary outcomes were chronologic and regional variation in SUP prescribing assessed by Joinpoint regression and Pearson's correlation. Rates of GI bleeding, gastritis, enteric ulceration, and SUP-related complications (C. difficile colitis, necrotizing enterocolitis, and thrombocytopenia) were compared for those with and without SUP exposure. RESULTS: Of 30 177 children studied, 10 387 (34.4%) received SUP. No episodes of GI bleeding were recorded. One subject developed gastric ulceration and 32 (0.1%) gastritis. Linear trends for SUP were observed with rates increasing from 25.5% in 2010 to 42.1% in 2019 (+1.9% annually). Prescribing varied by institution (range: 5.5% to 97.2%) without correlation to admission volumes. Extremely rare rates of SUP-related complications were noted. CONCLUSIONS: Although children hospitalized for CA routinely receive SUP, no episodes of GI bleeding were noted over a 10-year period. SUP solely for corticosteroid exposure may be unwarranted. We advocate for a targeted approach to SUP considering alternative risk factors for GI bleeding.

Transport of lysosomes decreases in the perinuclear region: Insights from changepoint analysis.

Lysosomes are membrane-bound organelles that serve as the endpoint for endocytosis, phagocytosis, and autophagy, degrading the molecules, pathogens, and organelles localized within them. These cellular functions require intracellular transport. We use fluorescence microscopy to characterize the motion of lysosomes as a function of intracellular region, perinuclear or periphery, and lysosome diameter. Single-particle tracking data are complemented by changepoint identification and analysis of a mathematical model for state switching. We first classify lysosomal motion as motile or stationary. We then study how lysosome location and diameter affects the proportion of time spent in each state and quantify the speed during motile periods. We find that the proportion of time spent stationary is strongly region dependent, with significantly decreased motility in the perinuclear region. Increased lysosome diameter only slightly decreases speed. Overall, these results demonstrate the importance of decomposing particle trajectories into qualitatively different behaviors before conducting population-wide statistical analysis. Our results suggest that intracellular region is an important factor to consider in studies of intracellular transport.

High-flow nasal cannula and bilevel positive airway pressure for pediatric status asthmaticus: a single center, retrospective descriptive and comparative cohort study.

INTRODUCTION: We aimed to describe patient characteristics and clinical outcomes for children hospitalized for status asthmaticus (SA) receiving high-flow nasal cannula (HFNC) or bilevel positive airway pressure (BiPAP). METHODS: We performed a single center, retrospective cohort study among 39 children admitted for SA aged 5-17 years from January 2016 to May 2019 to a quaternary pediatric intensive care unit (PICU). Cohorts were defined by BiPAP versus HFNC exposure and assessed to determine if differences existed in demographics, anthropometrics, comorbidities, asthma severity indices, historical factors, duration of noninvasive ventilation, and asthma-related clinical outcomes (i.e. length of stay, mechanical ventilation rates, exposure to concurrent sedatives/anxiolysis, and rate of adjunctive therapy exposure). RESULTS: Thirty-three percent (n = 13) received HFNC (33%) and 67% (n = 26) BiPAP. Children receiving BiPAP had greater age (10.9 ± 3.7 vs. 6.8 ± 2.2 years, P < 0.01), asthma severity (proportion with severe NHLBI classification: 38% vs. 0%, P < 0.01; median pediatric asthma severity score: 13[12,14] vs. 10[9,12], P < 0.01), previous PICU admissions (62% vs. 15%, P = 0.01), frequency of prescribed anxiolysis/sedation (42% vs. 8%, P = 0.02), and median duration of continuous albuterol (1.7[1,3.1] vs. 0.9[0.7,1.6] days, P = 0.03) compared to those on HFNC. Those on HFNC more commonly were treated comorbid bacterial pneumonia (69% vs. 19%, P < 0.01). No differences in NIV duration, mortality, mechanical ventilation rates, or LOS were observed. CONCLUSIONS: Our data suggest a trial of BiPAP or HFNC appears well tolerated in children with SA. Prospective trials are needed to establish modality superiority and identify patient or clinical characteristics that prompt use of HFNC over BiPAP.

A change point analysis protocol for comparing intracellular transport by different molecular motor combinations.

Intracellular transport by microtubule-based molecular motors is marked by qualitatively different behaviors. It is a long-standing and still-open challenge to accurately quantify the various individual-cargo behaviors and how they are affected by the presence or absence of particular motor families. In this work we introduce a protocol for analyzing change points in cargo trajectories that can be faithfully projected along the length of a (mostly) straight microtubule. Our protocol consists of automated identification of velocity change points, estimation of velocities during the behavior segments, and extrapolation to motor-specific velocity distributions. Using simulated data we show that our method compares favorably with existing methods. We then apply the technique to data sets in which quantum dots are transported by Kinesin-1, by Dynein-Dynactin-BicD2 (DDB), and by Kinesin-1/DDB pairs. In the end, we identify pausing behavior that is consistent with some tug-of-war model predictions, but also demonstrate that the simultaneous presence of antagonistic motors can lead to long processive runs that could contribute favorably to population-wide transport.

Leaf Economics of Early- and Late-Successional Plants.

AbstractThe leaf economics spectrum ranges from cheap, short-lived leaves to expensive, long-lived leaves. Species with low leaf mass per area (LMA) and short leaf life span tend to be fast growing and shade intolerant (early successional), whereas species with high LMA and long leaf life span tend to be slow growing and shade tolerant (late successional). However, we have limited understanding of how different leaf mass components (e.g., metabolically active photosynthetic components vs. structural toughness components) contribute to variation in LMA and other leaf economics spectrum traits. Here, we develop a model of plant community dynamics in which species differ in just two traits, photosynthetic and structural LMA components, and we identify optimal values of these traits for early- and late-successional species. Most of the predicted increase in LMA from early- to late-successional species was due to structural LMA. Photosynthetic LMA did not differ consistently between early- and late-successional species, but the photosynthetic LMA to structural LMA ratio declined from early- to late-successional species. Early-successional species had high rates of instantaneous return on leaf mass investment, whereas late-successional species had high lifetime return. Our results provide theoretical support for the primary role of structural (rather than photosynthetic) LMA variation in driving relationships among leaf economics spectrum traits.

The bronchiolitis severity score: An assessment of face validity, construct validity, and interobserver reliability.

OBJECTIVE: To assess face validity, interobserver reliability, and the ability to discriminate escalations of care within 24-h of admission (late rescues) for the bronchiolitis severity score (BSS) for children hospitalized for acute bronchiolitis. HYPOTHESES: The BSS will yield variable face validity, have clinically relevant interobserver reliability (kappa > 0.7), and distinguish late rescues during hospitalization. METHODS: We performed a combined retrospective and prospective, mixed methods study where (1) interobserver agreement was prospectively assessed by overall and subcategory congruence (kappa) calculations, (2) face value were qualitatively assessed from aggregate questionnaire responses, and (3) construct validity for late rescues were assessed using receiver operator characteristic (ROC) curve analyses. RESULTS: Face validity, assessed from 39 questionnaire respondents, were generally positive for BSS utility, reliability, and usability. The BSS exhibited weak interobserver reliability (kappa = 0.22, 95% confidence interval [CI]: 0.11-0.31) calculated from 72 sequential, blinded calculations. Retrospectively, 181 children less than 2 years of age admitted to the general pediatric ward for acute bronchiolitis from November 2017 to April 2019 were identified of which 18 (9.9%) experienced late rescues. Admission BSS values were no different for children with and without late rescues (6[3,6] vs. 4[3,6]; p = .09). An ROC curve analysis revealed an area under the curve of 0.61 (95% CI: 0.48-0.75; threshold ≥6 with sensitivity = 56%, specificity = 69%) for BSS to discriminate late rescues. CONCLUSION: Although clinicians expressed favorable perceptions of BSS face and content validity, we noted weak interobserver reliability and limited construct validity. Further development and validation are needed to strengthen the BSS before routine use.

Topological Data Analysis Approaches to Uncovering the Timing of Ring Structure Onset in Filamentous Networks.

In developmental biology as well as in other biological systems, emerging structure and organization can be captured using time-series data of protein locations. In analyzing this time-dependent data, it is a common challenge not only to determine whether topological features emerge, but also to identify the timing of their formation. For instance, in most cells, actin filaments interact with myosin motor proteins and organize into polymer networks and higher-order structures. Ring channels are examples of such structures that maintain constant diameters over time and play key roles in processes such as cell division, development, and wound healing. Given the limitations in studying interactions of actin with myosin in vivo, we generate time-series data of protein polymer interactions in cells using complex agent-based models. Since the data has a filamentous structure, we propose sampling along the actin filaments and analyzing the topological structure of the resulting point cloud at each time. Building on existing tools from persistent homology, we develop a topological data analysis (TDA) method that assesses effective ring generation in this dynamic data. This method connects topological features through time in a path that corresponds to emergence of organization in the data. In this work, we also propose methods for assessing whether the topological features of interest are significant and thus whether they contribute to the formation of an emerging hole (ring channel) in the simulated protein interactions. In particular, we use the MEDYAN simulation platform to show that this technique can distinguish between the actin cytoskeleton organization resulting from distinct motor protein binding parameters.

Pediatric asthma severity scores distinguish suitable inpatient level of care for children admitted for status asthmaticus.

Objective: To determine if the Pediatric Asthma Severity Score (PASS) can distinguish "late-rescues" (transfer to the pediatric intensive care unit [PICU] within 24-hours of general pediatric floor admission), "PICU readmissions" (readmission within 24-h after transfer to a lower inpatient level of care), and unplanned 30-day hospital readmission in children admitted with status asthmaticus.Methods: We performed a single center, retrospective cohort study in 328 children admitted for asthma exacerbation aged 5-18 years from May 2015 to October 2017. We sought to determine if PASS values preceding admission from the emergency department or transfer to the general pediatric unit will be greater in children with late rescues and PICU readmissions and if a cutoff PASS values exist to discriminate these events prior to intrafacility transfer.Results: Nine (5%) late-rescues and 5 (3%) PICU readmissions accounted for 14/328 (4%) composite outcomes. PASS values were greater in children with these events (8 [IQR:5-8] vs. 5 [IQR:3-6], p < .01). Logistic regression of PASS on composite outcome yielded an odds ratio of 1.4 (1.1-1.8, p < .01) and ROC curve of PASS on a composite outcome yielded an AUC of 0.74 (0.61-0.87) with a threshold of ≥ 9. Nine (3%) children experienced unplanned 30-day hospital readmissions but PASS preceding hospital discharge was neither discriminative nor associated with hospital readmission.Conclusions: PASS values ≥ 9 identify children at increased risk for late-rescue and PICU readmission. Applied with traditionally criteria for selection of inpatient level of care, PASS may assist providers in reducing acute inpatient disposition errors.

Physiometric Response to High-Flow Nasal Cannula Support in Acute Bronchiolitis.

OBJECTIVES: To describe the rate of high-flow nasal cannula (HFNC) nonresponse and paired physiometric responses (changes [∆] in heart rate [HR] and respiratory rate [RR]) before and after HFNC initiation in hospitalized children with bronchiolitis. METHODS: We performed a single-center, prospective descriptive study in a PICU within a quaternary referral center, assessing children aged ≤2 years admitted for bronchiolitis on HFNC from November 2017 to March 2020. We excluded for cystic fibrosis, airway anomalies, pulmonary hypertension, tracheostomy, neuromuscular disease, congenital heart disease, or preadmission intubation. Primary outcomes were paired ∆ and %∆ in HR and RR before and after HFNC initiation. Secondary outcomes were HFNC nonresponse rate (ie, intubation or transition to noninvasive positive pressure ventilation). Analyses included χ2, Student's t, Wilcoxon rank, and paired testing. RESULTS: Of the 172 children studied, 56 (32.6%) experienced HFNC nonresponse at a median of 14.4 (interquartile range: 4.8-36) hours and 11 (6.4%) were intubated. Nonresponders had a greater frequency of bacterial pneumonia, but otherwise no major differences in demographics, comorbidities, or viral pathogens were noted. Responders experienced reductions in both %ΔRR (-17.1% ± 15.8% vs +5.3% ± 22.3%) and %ΔHR (-6.5% ± 10.5% vs 0% ± 10.9%) compared with nonresponders. CONCLUSIONS: In this prospective, observational cohort study, we provide baseline data describing expected physiologic changes after initiation of HFNC for children admitted to the PICU for bronchiolitis. In our descriptive analysis, patients with comorbid bacterial pneumonia appear to be at additional risk for subsequent HFNC nonresponse.

Renewal Reward Perspective on Linear Switching Diffusion Systems in Models of Intracellular Transport.

In many biological systems, the movement of individual agents is characterized having multiple qualitatively distinct behaviors that arise from a variety of biophysical states. For example, in cells the movement of vesicles, organelles, and other intracellular cargo is affected by their binding to and unbinding from cytoskeletal filaments such as microtubules through molecular motor proteins. A typical goal of theoretical or numerical analysis of models of such systems is to investigate effective transport properties and their dependence on model parameters. While the effective velocity of particles undergoing switching diffusion dynamics is often easily characterized in terms of the long-time fraction of time that particles spend in each state, the calculation of the effective diffusivity is more complicated because it cannot be expressed simply in terms of a statistical average of the particle transport state at one moment of time. However, it is common that these systems are regenerative, in the sense that they can be decomposed into independent cycles marked by returns to a base state. Using decompositions of this kind, we calculate effective transport properties by computing the moments of the dynamics within each cycle and then applying renewal reward theory. This method provides a useful alternative large-time analysis to direct homogenization for linear advection-reaction-diffusion partial differential equation models. Moreover, it applies to a general class of semi-Markov processes and certain stochastic differential equations that arise in models of intracellular transport. Applications of the proposed renewal reward framework are illustrated for several case studies such as mRNA transport in developing oocytes and processive cargo movement by teams of molecular motor proteins.

Stress ulcer prophylaxis in children with status asthmaticus receiving systemic corticosteroids: a descriptive study assessing frequency of clinically important bleeding.

Objective: To determine the frequency of clinically important bleeding (CIB) among children hospitalized for status asthmaticus with and without exposure to stress ulcer prophylaxis (SUP).Methods: We performed a single-center, retrospective cohort in 217 children admitted for asthma exacerbation aged 5-18 years from May 2015 to May 2017. We assessed cohorts with and without exposure to SUP to determine if differences in frequency of CIB exist. Study outcomes included frequency of CIB, gastrointestinal complications (occult bleeding, macroscopic bleeding, gastric perforation, and acquired gastritis), and SUP-related adverse events (ventilator associated pneumonia, C. difficile colitis, necrotizing enterocolitis, and acute thrombocytopenia).Results: Ninety-two (42%) children received SUP of which 82 were admitted to the pediatric intensive care unit (PICU). There were no differences in asthma severity or known risk factors for CIB in children with and without SUP in the PICU subcohort. We observed no CIB or SUP-related adverse events. Two subjects acquired gastritis in the no-SUP cohort and one additional subject experienced occult gastrointestinal bleeding with spontaneous symptom resolution.Conclusion: Children admitted for status asthmaticus with and without SUP had no observed incidence of CIB. In this specific population, we propose a prerequisite assessment for the presence of known stress ulcer related gastrointestinal bleeding risk factors prior to the blanket administration of SUP.

Antibody-Mediated Immobilization of Virions in Mucus.

Antibodies have been shown to hinder the movement of herpes simplex virus virions in cervicovaginal mucus, as well as other viruses in other mucus secretions. However, it has not been possible to directly observe the mechanisms underlying this phenomenon, so the nature of virion-antibody-mucin interactions remain poorly understood. In this work, we analyzed thousands of virion traces from single particle tracking experiments to explicate how antibodies must cooperate to immobilize virions for relatively long time periods. First, using a clustering analysis, we observed a clear separation between two classes of virion behavior: freely diffusing and immobilized. While the proportion of freely diffusing virions decreased with antibody concentration, the magnitude of their diffusivity did not, implying an all-or-nothing dichotomy in the pathwise effect of the antibodies. Proceeding under the assumption that all binding events are reversible, we used a novel switch-point detection method to conclude that there are very few, if any, state switches on the experimental timescale of 20 s. To understand this slow state switching, we analyzed a recently proposed continuous-time Markov chain model for binding kinetics and virion movement. Model analysis implied that virion immobilization requires cooperation by multiple antibodies that are simultaneously bound to the virion and mucin matrix and that there is an entanglement phenomenon that accelerates antibody-mucin binding when a virion is immobilized. In addition to developing a widely applicable framework for analyzing multistate particle behavior, this work substantially enhances our mechanistic understanding of how antibodies can reinforce a mucus barrier against passive invasive species.

Assessing the Impact of Electrostatic Drag on Processive Molecular Motor Transport.

The bidirectional movement of intracellular cargo is usually described as a tug-of-war among opposite-directed families of molecular motors. While tug-of-war models have enjoyed some success, recent evidence suggests underlying motor interactions are more complex than previously understood. For example, these tug-of-war models fail to predict the counterintuitive phenomenon that inhibiting one family of motors can decrease the functionality of opposite-directed transport. In this paper, we use a stochastic differential equations modeling framework to explore one proposed physical mechanism, called microtubule tethering, that could play a role in this "co-dependence" among antagonistic motors. This hypothesis includes the possibility of a trade-off: weakly bound trailing molecular motors can serve as tethers for cargoes and processing motors, thereby enhancing motor-cargo run lengths along microtubules; however, this introduces a cost of processing at a lower mean velocity. By computing the small- and large-time mean-squared displacement of our theoretical model and comparing our results to experimental observations of dynein and its "helper protein" dynactin, we find some supporting evidence for microtubule tethering interactions. We extrapolate these findings to predict how dynein-dynactin might interact with the opposite-directed kinesin motors and introduce a criterion for when the trade-off is beneficial in simple systems.